JP2016222945A - Mixed powder for iron-based powder metallurgy and manufacturing method therefor, sintered body manufactured by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mixed powder for iron-based powder metallurgy capable of manufacturing a sintered body having stable quality and performance.SOLUTION: A mixed powder for iron-based powder metallurgy contains a powder containing anhydrous II type calcium sulfate so that weight ratio of CaS after sintering is 0.01 wt.% to 0.1 wt.%.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a mixed powder for iron-based powder metallurgy and a sintered body produced using the same, and a mixed powder for iron-based powder metallurgy containing anhydrous II-type calcium sulfate in a specific ratio and a sintered product produced using the same. Concerning union.

  Powder metallurgy is widely used as an industrial production method for various machine parts. The procedure for iron-based powder metallurgy is to first prepare a mixed powder by mixing an iron-based powder, an alloy powder such as a copper (Cu) powder, a nickel (Ni) powder, a graphite powder, and a lubricant. . Next, the mixed powder is filled into a mold, press-molded, and sintered to produce a sintered body. Then, a machine part having a desired shape is prepared by performing cutting such as drilling or turning on the sintered body.

  The ideal of powder metallurgy is to process the sintered body so that it can be used as a machine part without cutting the sintered body. However, the sintering may cause uneven shrinkage of the raw material powder, and in recent years, the dimensional accuracy required for mechanical parts is high, and the part shape may be complicated. For this reason, it is becoming essential to cut the sintered body. From such a technical background, a technique for imparting machinability to a sintered body has been studied so that the sintered body can be processed smoothly.

  As means for imparting the machinability, there is a technique of adding manganese sulfide (MnS) powder to the mixed powder. The addition of manganese sulfide powder is effective for relatively low speed cutting such as drilling. However, the addition of manganese sulfide powder is not necessarily effective in recent high-speed cutting, and there are problems such as generation of dirt on the sintered body and reduction in mechanical strength.

  For this reason, as a document disclosing a method for imparting machinability other than adding the above-mentioned manganese sulfide, for example, Patent Document 1 discloses that iron-based raw material powder containing a necessary amount of iron powder and copper is contained. Sintered steel containing 0.1 to 1.0% calcium sulfide (CaS), 0.1 to 2% carbon (C), and 0.5 to 5.0% copper (Cu) Is disclosed.

Japanese Patent Publication No. 52-16684

  By including the calcium sulfide disclosed in Patent Document 1, there are problems such that the strength of mechanical parts is significantly reduced, and that the mixed powder changes with time and the quality is not stable. Moreover, when the sintered steel disclosed in Patent Document 1 was processed with a cutting tool, it was difficult for the chips to be finely divided. From this, it is difficult to say that the chip disposability evaluated as good in the disclosure of Patent Document 1 is excellent enough to satisfy the current chip disposability requirements.

  This invention is made | formed in view of said subject, The place made into the objective is providing the mixed powder for iron-base powder metallurgy which can produce the sintered compact of the stable quality and performance.

In order to achieve the above object, the present inventor investigated why the quality and performance of the sintered body disclosed in Patent Document 1 deteriorated with the passage of time. These two components are described as “CaS component”). That is, the present inventor changed the calcium sulfate component to calcium sulfate dihydrate (CaSO ₄ .2H ₂ O) by absorbing moisture in the atmosphere, or the CaS component aggregated by a curing reaction to cause a coarse particle size of 63 μm or more. It was found that grains were formed. As a result, the CaS component is dispersed unevenly in the mixed powder or the sintered body to reduce the machinability of the sintered body, or the moisture adsorbed on the CaS component expands during the sintering and the strength of the sintered body It became clear that it lowered.

  Based on the above findings, the present invention shown below was completed by further diligently examining the crystal structure of calcium sulfate having low hygroscopicity.

  That is, in the mixed powder for iron-based powder metallurgy according to the present invention, the weight ratio of CaS after sintering powder containing anhydrous type II calcium sulfate is 0.01 wt% or more and 0.1 wt% or less. It is characterized by including.

Since anhydrous type II calcium sulfate has low hygroscopicity and does not absorb moisture in the atmosphere, powder containing anhydrous type II calcium sulfate (also referred to as “type II CaSO ₄ powder”) is stored in the atmosphere for a certain period of time. Even if mass does not increase. For this reason, by using powder containing anhydrous type II calcium sulfate instead of calcium sulfide and hemihydrate gypsum as a component to be sintered into CaS, various performances of the sintered body can be stably improved. .

The type II CaSO ₄ powder preferably has a volume average particle size of 0.1 μm or more and 60 μm or less. By having such a volume average particle diameter, the machinability of the sintered body can be enhanced.

When the volume average particle diameter of the type II CaSO ₄ powder is R μm and the weight ratio of CaS contained in the sintered body after sintering is W wt%, R ^1/3 / W is 15 or more and 400 or less. Is preferred. By satisfying this numerical range, it is possible to obtain a sintered body having good crushing strength, machinability, and chip treatability.

  The mixed powder for iron-based powder metallurgy according to the present invention may further include one or more ternary oxides selected from the group consisting of Ca—Al—Si oxides and Ca—Mg—Si oxides. preferable. By including such a ternary oxide, the machinability in long-time cutting can be improved.

  The weight ratio of the ternary oxide to CaS after sintering is preferably 3: 7 to 9: 1. By using a powder containing a ternary oxide and anhydrous type II calcium sulfate in such a weight ratio, the machinability in long-term cutting can be improved.

Type II CaSO ₄ powder may be coated with a lubricant or a binder.

  The present invention is a sintered body produced by sintering the mixed powder for iron-based powder metallurgy. A sintered body produced using the above mixed powder for iron-based powder metallurgy is stably excellent in various properties such as machinability.

  The method for producing a mixed powder for iron-based powder metallurgy according to the present invention is a step of producing a powder containing anhydrous type II calcium sulfate by heating a powder containing dihydrate gypsum or hemihydrate gypsum at 350 ° C. or more and 900 ° C. or less. And mixing the powder containing the anhydrous type II calcium sulfate and the iron-based powder. The mixed powder for iron-based powder metallurgy thus produced exhibits stable performance because it is difficult to absorb moisture.

  ADVANTAGE OF THE INVENTION According to this invention, the mixed powder for iron base powder metallurgy which can produce the sintered compact of the stable performance can be provided.

It is an image which shows an example of the external appearance of the chip | tip with favorable chip | tip processing property. It is an image which shows an example of the external appearance of the chip | tip whose chip disposal property is not favorable. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Example 26 with the cermet chip. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Example 30 with the cermet chip. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Example 32 with the cermet chip. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Example 33 with the cermet chip. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Example 34 with the cermet chip. It is an observation image of the wear part of the tool rake face after turning the sintered compact produced in Reference Example 1 with a cermet chip.

  Hereinafter, the mixed powder for iron-based powder metallurgy according to the present invention and the production method thereof will be described in detail.

<Mixed powder for iron-based powder metallurgy>
The mixed powder for iron-based powder metallurgy of the present invention is a mixed powder obtained by mixing an iron-based powder and a powder containing anhydrous type II calcium sulfate (hereinafter also referred to as “type II CaSO ₄ powder”). Various additives such as a ternary oxide, a binary oxide, an alloy powder, a graphite powder, a lubricant, and a binder may be appropriately added to the mixed powder. In addition to these, a trace amount of inevitable impurities may be included in the production process of the mixed powder for iron-based powder metallurgy. The mixed powder for iron-based powder metallurgy according to the present invention can be obtained by filling a metal mold or the like and molding it, followed by sintering. The sintered body produced in this way can be used for various machine parts by cutting. The use and manufacturing method of this sintered body will be described later.

<Iron-based powder>
The iron-based powder is a main component constituting the mixed powder for iron-based powder metallurgy, and is preferably contained in a weight ratio of 60% by weight or more with respect to the entire mixed powder for iron-based powder metallurgy. In addition, the weight% of iron-base powder here means the ratio for the total weight other than a lubricant among the mixed powder for iron-base powder metallurgy. In the following, when the weight percent of each component is defined, the definition means the weight ratio in the total weight of the iron-based powder metallurgy mixed powder excluding the lubricant.

  As the iron-based powder, atomized iron powder, pure iron powder such as reduced iron powder, partially diffusion alloyed steel powder, fully alloyed steel powder, or hybrid steel powder in which alloy components are partially diffused Etc. can be used. The volume average particle diameter of the iron-based powder is preferably 50 μm or more, more preferably 70 μm or more. When the iron-based powder is 50 μm or more, the handling property is excellent. The volume average particle size of the iron-based powder is preferably 200 μm or less, and more preferably 100 μm or less. When it is 200 μm or less, it is easy to form a precise shape and sufficient strength can be obtained.

<II type CaSO ₄ powder>
The mixed powder for iron-based powder metallurgy according to the present invention includes a powder containing anhydrous type II calcium sulfate (type II CaSO ₄ powder). The present invention overturns the conventional technical common sense (for example, Patent Document 1), which has been considered that the machinability of a sintered body can be improved only by adding a component that becomes calcium sulfide (CaS) after sintering. is there. That is, as raw materials to be sintered into CaS, dihydrate gypsum (CaSO ₄ .2H ₂ O), anhydrous type III calcium sulfate (III type CaSO ₄ ), hemihydrate gypsum (CaSO ₄ .1 / 2H ₂ O) However, each of these components may absorb moisture with time and may reduce the machinability of the sintered body. On the other hand, anhydrous type II calcium sulfate has low hygroscopicity and does not absorb moisture in the atmosphere, so the mass may increase even if it is stored for a certain period in a state of being contained in the iron-based powder metallurgy mixed powder. Absent. In addition, anhydrous type II calcium sulfate can be changed to CaS after sintering to enhance the machinability of the sintered body. For this reason, the mixed powder for iron-based powder metallurgy containing II-type CaSO ₄ powder can stably improve various performances of the sintered body as compared with other components that are sintered to become CaS.

Type II CaSO ₄ powder contains anhydrous type II calcium sulfate as a main component, but dihydrate gypsum (CaSO ₄ .2H ₂ O), anhydrous type III calcium sulfate (type III CaSO ₄ ), hemihydrate gypsum ( CaSO ₄ · 1 / 2H ₂ O) or the like may be contained. However, it is preferable that the type II CaSO ₄ powder has a higher weight ratio of anhydrous type II calcium sulfate, more preferably the weight percentage of anhydrous type II calcium sulfate is 70% by weight or more, and more preferably 80% by weight. % Or more, particularly preferably consisting of anhydrous type II calcium sulfate alone. Further, the surface of the type II CaSO ₄ powder may be coated with a lubricant or a binder described later.

The type II CaSO ₄ powder is preferably contained in the iron-based powder metallurgy mixed powder so that the weight ratio of CaS after sintering is 0.01 wt% or more and 0.1 wt% or less. In the type II CaSO ₄ powder, the weight ratio of CaS after sintering is more preferably 0.02% by weight or more, and the weight ratio of CaS after sintering is more preferably 0.03% by weight or more. A sintered body containing CaS at such a weight ratio is particularly excellent in machinability. On the other hand, type II CaSO ₄ powder is contained so that the weight ratio of CaS after sintering is 0.09 wt% or less, more preferably 0.08 wt% or less. By including CaS at such a weight ratio, the strength of the sintered body can be increased.

Here, “weight ratio of CaS after sintering” means the weight ratio of CaS in the sintered body obtained by sintering the mixed powder for iron-based powder metallurgy. The weight ratio of CaS contained in the sintered body after sintering can be adjusted by the weight ratio of type II CaSO ₄ powder contained before sintering.

  The weight ratio of CaS contained in the sintered body is the weight of Ca obtained by taking a sample piece by processing the sintered body with a drill or the like and quantitatively analyzing the weight of Ca contained in the sample piece. It can be calculated by converting to the weight of CaS. This conversion is performed by integrating the molecular weight of CaS (72.143) by dividing by the atomic weight of Ca (40.078). This is because Ca hardly reacts and disappears during sintering, so the weight of Ca does not change before and after sintering, and Ca and S are combined at 1: 1.

The volume average particle diameter of the type II CaSO ₄ powder is preferably 0.1 μm or more, more preferably 0.5 μm or more, and further preferably 1 μm or more. The volume average particle size of the type II CaSO ₄ powder is preferably 60 μm or less, more preferably 30 μm or less, and still more preferably 20 μm or less. Such a type II CaSO ₄ powder having a volume average particle diameter can be obtained, for example, by heating and maintaining hemihydrate gypsum to 350 ° C. or more and 900 ° C. or less and pulverizing and classifying what is held for 1 hour or more and 10 hours or less. it can. As the volume average particle diameter of type II CaSO ₄ powder is small, even if a small amount the amount of type II CaSO ₄ powder can improve the machinability of the sintered body. The volume average particle size is a value of the particle size D ₅₀ of 50% of the integrated value in the particle size distribution obtained using a laser diffraction particle size distribution measuring apparatus (Nikkiso Microtrack “MODEL 9320-X100”).

When the volume average particle diameter of type II CaSO ₄ powder is R (μm) and the weight ratio of CaS contained in the sintered body after sintering is W (wt%), the lower limit of R ^1/3 / W is 15 It is preferable that it is above, More preferably, it is 20 or more, More preferably, it is 25 or more. The upper limit of R ^1/3 / W is preferably 400 or less, more preferably 340 or less, and even more preferably 270 or less. The technical basis of such a definition is not necessarily clear, but the present inventor believes that the relationship between the volume average particle diameter and the weight ratio, which is proportional to the cube root of the volume ratio, probably correlates with various properties of the sintered body. Based on experience. By satisfying such a numerical range, a sintered body having good crushing strength, machinability and chip treatability can be obtained.

<Ternary oxide>
The ternary oxide may be added to improve machinability when the sintered body is used for cutting for a long time. The ternary oxide can remarkably enhance the machinability of the sintered body in combination with the addition of the type II CaSO ₄ powder. Here, the ternary oxide means a composite oxide of three elements, specifically selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe and Zn. It is preferable to use a composite oxide of these three elements, more preferably a Ca—Al—Si oxide, a Ca—Mg—Si oxide, or the like. The Ca-Al-Si-based oxides, _{2CaO · Al 2 O 3 · SiO} 2 or the like. Examples of the Ca—Mg—Si oxide include 2CaO · MgO · 2SiO ₂ . Among these it is preferable to add _{2CaO · Al 2 O 3 · SiO} 2. The _{2CaO · Al 2 O 3 · SiO} 2 reacts with TiO ₂ contained in the coating applied in the cutting tool or cutting tool, forming a protective film on the surface of the cutting tool, wear resistance of the cutting tool Can be significantly improved.

  The shape of the ternary oxide is not particularly limited, but a spherical shape or a shape in which it is crushed, that is, a shape having a round shape as a whole is preferable.

The lower limit of the volume average particle diameter of the ternary oxide is preferably 0.1 μm or more, more preferably 0.5 μm or more, and further preferably 1 μm or more. As the volume average particle size is smaller, there is a tendency that the machinability of the sintered body can be improved by adding a small amount. Further, the upper limit of the volume average particle diameter of the ternary oxide is preferably 15 μm or less, more preferably 10 μm or less, and still more preferably 9 μm or less. When the volume average particle diameter is too large, it becomes difficult to improve the machinability of the sintered body. The volume average particle diameter of the ternary oxide is a value measured by the same measurement method as that for the type II CaSO ₄ powder.

The lower limit of the content of the ternary oxide is preferably 0.01% by weight or more, more preferably 0.03% by weight or more, and still more preferably 0.05% by weight or more. Further, the upper limit of the content of the ternary oxide is preferably 0.25% by weight or less, more preferably 0.2% by weight or less, and further preferably 0.15% by weight or less. By including in such a weight ratio, a sintered body excellent in machinability can be obtained even during long-term cutting while suppressing cost. By using a ternary oxide in combination with II-type CaSO ₄ powder as in the present invention, the machinability in long-term cutting can be improved even if the addition amount of the ternary oxide is small. .

  The weight ratio of the ternary oxide to the sintered CaS is preferably included in a ratio of 1: 9 to 9: 1, more preferably 3: 7 to 9: 1, and still more preferably 4: 6 to 7: 3. By including both components in such a weight ratio, the machinability of the sintered body can be significantly improved.

<Binary oxide>
The binary oxide may be added to improve the machinability at the initial cutting when the sintered body is used for cutting. Here, the binary oxide means a composite oxide of two elements, specifically selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe and Zn. It is preferable to use a composite oxide of two kinds of elements, more preferably a Ca—Al oxide, a Ca—Si oxide, and the like. Examples of the Ca—Al-based oxide include CaO · Al ₂ O ₃ and 12CaO · 7Al ₂ O ₃ . Examples of the Ca—Si-based oxide include 2CaO · SiO ₂ .

  It is preferable that the shape, volume average particle diameter, measurement method, and weight ratio of the binary oxide are the same as those of the ternary oxide.

<Binary oxide and ternary oxide>
The mixed powder for iron-based powder metallurgy of the present invention preferably contains 0.02 wt% or more and 0.3 wt% or less of both binary oxide and ternary oxide in terms of the total weight. The total weight of the oxides is preferably 0.05% by weight or more, and more preferably 0.1% by weight or more. From the viewpoint of cost, the smaller the weight ratio of the binary oxide and the ternary oxide, the better. The total weight of the oxides is preferably 0.25% by weight or less, more preferably 0.2% by weight or less. When the total weight of the oxides is 0.25% by weight or less, the crushing strength of the sintered body can be sufficiently ensured.

  The weight ratio of the binary oxide and the sintered CaS is preferably included in a ratio of 1: 9 to 9: 1, more preferably 3: 6 to 9: 1, and still more preferably 4: 6 to 7. : 3. By including both components in such a weight ratio, a sintered body excellent in machinability at the initial stage of cutting can be produced.

<Alloy powder>
The alloy powder is added to promote bonding between the iron-based powders and to increase the strength of the sintered body after sintering. Such an alloy powder is preferably contained in an amount of 0.1 wt% or more and 10 wt% or less with respect to the entire mixed powder for iron-based powder metallurgy. When the content is 0.1% by weight or more, the strength of the sintered body can be increased, and when the content is 10% by weight or less, dimensional accuracy during sintering of the sintered body can be ensured.

  Examples of the alloy powder include non-ferrous metal powders such as copper (Cu) powder, nickel (Ni) powder, Mo powder, Cr powder, V powder, Si powder, and Mn powder, and cuprous oxide powder. You may use individually by 1 type and may use 2 or more types together.

<Lubricant>
The lubricant is added in order to make it easy to take out the molded body obtained by compressing the mixed powder for iron-based powder metallurgy in the mold. That is, when a lubricant is added to the mixed powder for iron-based powder metallurgy, it is possible to reduce the drawing pressure when taking out the molded body from the mold, and to prevent cracking of the molded body and damage to the mold. The lubricant may be added to the iron-based powder metallurgy mixed powder, or may be applied to the surface of the mold. When the lubricant is added to the iron-based powder metallurgy mixed powder, the lubricant is preferably contained in an amount of 0.01% by mass to 1.5% by mass with respect to the weight of the iron-based powder metallurgy mixed powder. More preferably, it is contained in an amount of from 1% by mass to 1.2% by mass, and more preferably from 0.2% by mass to 1.0% by mass. When the content of the lubricant is 0.01% by mass or more, it is easy to obtain an effect of reducing the punching pressure of the molded body. When the content of the lubricant is 1.5% by mass or less, a high-density sintered body can be easily obtained and a high-strength sintered body can be obtained.

  The lubricant is selected from the group consisting of metal soap (lithium stearate, calcium stearate, zinc stearate, etc.), stearic acid monoamide, fatty acid amide, amide wax, hydrocarbon wax and cross-linked (meth) acrylic acid alkyl ester resin. One or more of them can be used. Among these, it is preferable to use an amide-based lubricant from the viewpoint that the performance of attaching the alloy powder, the graphite powder, and the like to the surface of the iron-based powder is good and the segregation of the iron-based mixed powder is easily reduced.

<Binder>
The binder is added to adhere the alloy powder, the graphite powder and the like to the iron-based powder surface. As the binder, a butene polymer, a methacrylic acid polymer, or the like is used. As the butene polymer, it is preferable to use a 1-butene homopolymer consisting of butene alone or a copolymer of butene and alkene. The alkene is preferably a lower alkene, preferably ethylene or propylene. The methacrylic acid polymer is selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, ethyl hexyl methacrylate, lauryl methacrylate, methyl acrylate and ethyl acrylate 1 More than seeds can be used.

  The binder content is preferably 0.01% by mass or more and 0.5% by mass or less, and more preferably 0.05% by mass or more and 0.4% by mass or less, based on the weight of the mixed powder for iron-based powder metallurgy. More preferably, it is more preferably 0.1% by mass or more and 0.3% by mass or less.

<Method for producing mixed powder for iron-based powder metallurgy>
In the preparation of the mixed powder for iron-based powder metallurgy according to the present invention, first, a type II CaSO ₄ powder contained in the mixed powder for iron-based powder metallurgy is prepared. The type II CaSO ₄ powder is preferably obtained by heating hemihydrate gypsum or dihydrate gypsum having a volume average particle size of 0.1 μm or more and 60 μm or less at 300 ° C. or more and 900 ° C. or less. The volume average particle diameter of hemihydrate gypsum or dihydrate gypsum is preferably the same or slightly smaller than the volume average particle diameter of type II CaSO ₄ powder in consideration of aggregation during heating. The lower limit of the heating temperature is preferably 350 ° C. or higher, more preferably 400 ° C. or higher. Moreover, it is preferable that the upper limit of heating temperature is 800 degrees C or less, More preferably, it is 700 degrees C or less, More preferably, it is 500 degrees C or less. When the heating temperature is 900 ° C. or less, a type II CaSO ₄ powder having a particle diameter of 100 μm or less, which is a typical powder to be mixed with the iron-based powder, can be obtained. In particular, when the heating temperature is 700 ° C. or less, it is difficult for agglomeration of hemihydrate gypsum or dihydrate gypsum, and it is possible to obtain type II CaSO ₄ powder while maintaining the volume average particle diameter of hemihydrate gypsum or dihydrate gypsum. it can. When the heating temperature is high, strong agglomeration occurs, so that the pulverization step is preferably performed. When the heating temperature is 300 ° C. or higher, the water content of the hemihydrate gypsum or dihydrate gypsum can be dehydrated to obtain a type II CaSO ₄ powder. If the heating temperature is low, anhydrous III-type CaSO ₄ may be formed instead of anhydrous II-type CaSO ₄ , which is not preferable.

  The heating time is preferably secured for a time during which hemihydrate gypsum or dihydrate gypsum can be dehydrated into type II calcium sulfate, and preferably 1 hour or more and 8 hours or less. The higher the heating temperature, the shorter the heating time. When the heating time is short, part of the hemihydrate gypsum may remain as hemihydrate gypsum without changing to type II calcium sulfate, or may change to anhydrous type III calcium sulfate. For this reason, it is preferable that heating time is 2 hours or more, More preferably, it is 3 hours or more.

The mixed powder for iron-based powder metallurgy according to the present invention can be produced by mixing the iron-based powder and the type II CaSO ₄ powder produced above using, for example, a mechanical stirring mixer. In addition to these powders, various additives such as ternary oxides, alloy powders, graphite powders, lubricants, binary oxides, and binders may be added as appropriate. Examples of the mechanical stirring mixer include a high speed mixer, a nauter mixer, a V-type mixer, and a double cone blender. The order of mixing the powders is not particularly limited. The mixing temperature is not particularly limited, but is preferably 150 ° C. or lower from the viewpoint of suppressing oxidation of the iron-based powder in the mixing step.

<Method for producing sintered body>
After the mixed powder for iron-based powder metallurgy prepared above is filled in a mold, a compacted body is manufactured by applying a pressure of 300 MPa to 1200 MPa. The molding temperature at this time is preferably 25 ° C. or higher and 150 ° C. or lower.

  A sintered compact can be obtained by sintering the compacting body produced above by a normal sintering method. The sintering condition may be a non-oxidizing atmosphere or a reducing atmosphere, but under a nitrogen atmosphere, a mixed atmosphere of nitrogen and hydrogen, an atmosphere of hydrocarbon, etc., at a temperature of 1000 ° C. to 1300 ° C. for 5 minutes to 60 minutes. It is preferable to perform the following sintering.

<Sintered body>
The sintered body produced as described above can be used as machine parts such as automobiles, agricultural equipment, electric tools, and home appliances by processing with various tools such as cutting tools as necessary. Examples of the cutting tool for processing the sintered body include a drill, an end mill, a milling cutting tool, a turning cutting tool, a reamer, and a tap.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
First, commercially available hemihydrate gypsum powder was classified with a sieve to obtain −63 / + 45 μm (volume average particle diameter of 54 μm). The classified hemihydrate gypsum was heated at 350 ° C. for 5 hours in an atmospheric heating furnace to obtain anhydrous type II calcium sulfate powder (type II CaSO ₄ powder). This type II CaSO ₄ powder was classified with a sieve to obtain −63 / + 45 μm (volume average particle diameter 54 μm). The yield of the obtained type II CaSO ₄ powder was 100%. This yield is a value obtained by calculating the percentage of the weight of the type II CaSO ₄ powder after heating minus the weight of the type II CaSO ₄ powder removed by classification from the weight.

Next, with respect to pure iron powder (product name: Atmel 300M (manufactured by Kobe Steel, Ltd.)), 2% by weight of copper powder (product name: CuATW-250 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)) and 0.8 wt% graphite powder (product name CPB (manufactured by Nippon Graphite Industry Co., Ltd.)) and 0.75 wt% amide-based lubricant (Accra Wax C (manufactured by LONZA)) A mixed powder for iron-based powder metallurgy was prepared by mixing II type CaSO ₄ powder. The graphite powder was added in an amount such that the amount of carbon after sintering was 0.75% by weight. The type II CaSO ₄ powder was added in an amount such that the weight of CaS after sintering was 0.5% by weight.

  Two types of sintered bodies were prepared using the iron-based powder metallurgy mixed powder. One is a sintered body (hereinafter referred to as “immediately sintered body”) prepared using a mixed powder for iron-based powder metallurgy immediately after production, and the other is a mixed powder for iron-based powder metallurgy. 1 to 10 days from the date of storage in the air (hereinafter referred to as “sintered body after 10 days”).

Immediately after the production process of the sintered body, the mixed powder for iron-based powder metallurgy immediately after production was filled in a mold, and the ring shape was an outer diameter of 64 mm, an inner diameter of 24 mm, and a thickness of 20 mm, and the molding density was 7.00 g / cm ³ A test piece was molded so that Next, this ring-shaped test piece was sintered at 1130 ° C. for 30 minutes in a 10 volume% H ₂ —N ₂ atmosphere to produce a sintered body. On the other hand, the procedure for preparing the sintered body after 10 days was the same as that of the immediately after sintered body, except that the mold was filled with iron-based powder metallurgy mixed powder and left in the atmosphere for 10 days. Thus, a sintered body was produced.

(Examples 2 to 8)
A sintered body was produced in the same manner as in Example 1 except that the heating temperature of the hemihydrate gypsum powder was changed as shown in the column of “Heat treatment temperature” in Table 1.

(Comparative Examples 1-3)
A sintered body was produced in the same manner as in Example 1, except that anhydrous type II calcium sulfate was changed to the material shown in the column “CaS component” in Table 1. Comparative Example 1 produced a sintered body in the same manner as in Example 1 except that anhydrous type II calcium sulfate was not added.

<Evaluation>
In Table 1, the evaluation results of the green body density, the sintered body density, the crushing strength, and the tool wear amount are shown as “immediately sintered body / 10 days after sintered body”. In this notation, the value on the left side with the slash sandwiched is the evaluation result of the sintered body immediately after, and the value on the right side with the slash sandwiched is the evaluation result of the sintered body after 10 days.

  The values measured according to Japan Powder Metallurgy Industry Association Standard (JPMA M 01) were adopted for the compact density and sintered density of the sintered bodies immediately after each Example and each Comparative Example and after 10 days. For the crushing strength, a value obtained by measuring each sintered body of each example and each comparative example according to JIS Z 2507-2000 was adopted. It shows that the higher the crushing strength, the harder the sintered body is broken and the higher the strength.

  Using the sintered body produced in each example and each comparative example, using a cermet chip (ISO model number: SNGN120408 non-breaker), peripheral speed 160 m / min, cutting 0.5 mm / pass, feed 0.1 mm / The tool wear amount (μm) of the cutting tool when turning 1150 m under rev and dry conditions was measured with a tool microscope. The result is shown in the column of “Tool wear” in Table 1. In addition, it has shown that the machinability of a sintered compact is excellent, so that the value of tool wear amount is small.

From the results of each Example and each Comparative Example shown in Table 1, by including II-type CaSO ₄ powder as a CaS component as in each Example, various characteristics (sintered) It was found that the body density, the crushing strength, and the amount of tool wear were almost equal. On the other hand, since Comparative Examples 2 and 3 contain CaS alone or hemihydrate gypsum as the CaS component, the various properties of the sintered body after 10 days were significantly deteriorated compared to those of the immediately sintered body.

  The reason why the quality and performance of the sintered body deteriorated after 10 days in Comparative Examples 2 and 3 was that CaS in the iron-based powder metallurgy mixed powder or half-sintered while the iron-based powder metallurgy mixed powder was left for 10 days. This is probably because the water gypsum absorbed water. In other words, in Comparative Examples 2 and 3, the density of the sintered body decreases due to the CaS simple substance or hemihydrate gypsum in the mixed powder for iron-based powder metallurgy absorbing water during storage in the atmosphere for 10 days. It is considered that the crushing strength has decreased. Since Comparative Example 1 does not contain a CaS component, both the immediately sintered body and the sintered body after 10 days have significantly high tool wear, and the machinability of the sintered body is significantly low.

  Further, the sintered body after 10 days of Example 8 has various performances deteriorated as compared with those of Examples 1 to 7 as compared with the immediately after sintered body. This is because the heating temperature for the hemihydrate gypsum of Example 8 was lower than that of Examples 1-7, so that part of the hemihydrate gypsum did not change to type II calcium sulfate, and type III sulfuric acid. This may be due to the change to calcium or remaining as hemihydrate gypsum and the hygroscopic nature of these components. However, the stability of various performances of the sintered body obtained in Example 8 is remarkably superior to that of Comparative Examples 1 to 3. For this reason, as in Example 8, it was revealed that the effect of improving the stability of the sintered body can be obtained even if the entire hemihydrate gypsum is not made of type II calcium sulfate.

  When attention is paid to the “yield” of Examples 1 to 7 in Table 1, the yield tends to decrease as the heating temperature of the hemihydrate gypsum increases. The cause of this is considered to be that the higher the heating temperature, the more the II-type calcium sulfate agglomerates into large particles, and the large particles were removed by classification. Therefore, in order to efficiently obtain a powder composed of II-type calcium sulfate, it has become clear that the heating temperature of the hemihydrate gypsum is preferably 350 ° C. or higher and 600 ° C. or lower.

From the results shown in Table 1, by including type II CaSO ₄ powder as the CaS component, various properties (sintered body density, pressure ring strength and tool wear amount) of the sintered body immediately after and the sintered body after 10 days are almost equal. It became clear that the quality and performance of the sintered body were stable, and the effect of the present invention was shown.

(Examples 9 to 29)
Implementation was performed except that the volume average particle diameter of type II CaSO ₄ powder and the weight ratio of CaS after sintering were changed as shown in the columns of “volume average particle diameter” and “CaS weight ratio” in Table 2. A sintered body was produced in the same manner as in Example 1, and each item was evaluated by the same method as in Example 1. The results are shown in Table 2. Adjustment of the volume average particle diameter of the type II CaSO ₄ powder used in each example was performed by variously crushing and classifying the heat-treated type II CaSO ₄ powder.

  In Examples 9 to 29, as in Example 1 above, two types of sintered body immediately after and sintered body after 10 days were prepared and the respective characteristics were evaluated. Since it was the same or negligible difference, only one measured value is shown in Table 2. Therefore, it became clear that the sintered compact produced using the mixed powder for iron-base powder metallurgy of Examples 9-29 was stable in quality and performance, and the effects of the present invention were shown.

  “Chip treatability” in Table 2 is a result of evaluating the appearance of chips generated by turning using a cermet tip based on the following evaluation criteria.

(Evaluation criteria for chip disposal)
A: The number of spring-like turns (the number of curls) is 1 or less (for example, FIG. 1).
○: The curl number is within 1 to 3 turns.
X: The curl number exceeds 3 windings (for example, FIG. 2).

  When the chips are finely divided as shown in FIG. 1, the frequency of cleaning the chip hopper of the cutting machine can be suppressed. On the other hand, as shown in FIG. 2, if the chips extend long in a coil shape, the chips are complicatedly entangled in the chip hopper, and the trouble of cleaning becomes complicated, or the frequency of cleaning the chip hopper increases. Therefore, even if the amount of tool wear is reduced, long-term automatic operation is not possible, and it is difficult to save labor and improve efficiency.

From the results shown in Table 2, it is clear that when R ^1/3 / W is 20 or more and 340 or less, it is possible to produce a sintered body having excellent crushing strength, tool wear amount, and chip treatability. It became. On the other hand, if R ^1/3 / W is less than 20, the chip disposability tends to decrease, if R ^1/3 / W exceeds 340, the crushing strength tends to increase, and the tool wear tends to increase significantly. It was done.

(Examples 30-34 and Reference Examples 1-2)
Embodiment Example 30-34, a portion of the Type II CaSO ₄ powder as shown in Table _{3, 2CaO · Al 2 O 3} · SiO 2 or 2CaO · MgO · 2SiO other are different that instead of ₂ Example 26 A sintered body was produced in the same manner as described above. Reference Examples 1 and 2 were sintered in the same manner as in Example 26 except that all of the type II CaSO ₄ powder was replaced with 2CaO · Al ₂ O ₃ · SiO ₂ or 2CaO · MgO · 2SiO ₂ , respectively. The body was made. 2CaO · Al ₂ O ₃ · SiO ₂ and 2CaO · MgO · 2SiO ₂ having a volume average particle diameter of 2 μm were used. The type II CaSO ₄ powder used had a volume average particle diameter of 18.4 μm.

  Each item was evaluated by the same method as in Example 26 for the sintered bodies of Examples and Comparative Examples thus produced. The results are shown in Table 3. In Examples 30 to 34, two types of sintered body immediately after and sintered body after 10 days were prepared and their characteristics were evaluated. However, both measured values were the same or negligible in all evaluation items. Because of the difference, only one measurement value is shown in Table 3. Therefore, it became clear that the quality and performance of the sintered compact produced using the mixed powder for iron-based powder metallurgy of Examples 30 to 34 were stable, and the effect of the present invention was shown.

From the results shown in Table 3, the amount of tool wear can be further reduced by substituting a part of the type II CaSO ₄ powder with a ternary oxide, and in particular, as shown in the results of Examples 32-34, 3 It was found that the amount of tool wear can be significantly reduced when the weight ratio of the base oxide to the sintered CaS is from 3: 7 to 9: 1.

The reason why the amount of tool wear can be reduced in this way is considered to be due to the interaction between the two types of CaSO ₄ powder and the ternary oxide.

The reason for thinking in this way is that when the type II CaSO ₄ powder and the ternary oxide are used in combination, the wear form of the tool rake face and the component of the worn part differ between the case of the ternary oxide alone. is there. 3 to 8 are images obtained by observing, with an optical microscope, a worn portion of the tool rake face after turning the sintered bodies produced in Examples 26, 30, 32 to 34 and Reference Example 1 with a cermet tip. . As shown in FIGS. 4 to 7, when the II type CaSO ₄ powder and the ternary oxide are used in combination (Examples 30, 32 to 34), iron adhesion is reduced and groove-like wear is observed. There wasn't. On the other hand, when only the ternary oxide is added without adding the type II CaSO ₄ powder (Reference Example 1), as shown in FIG. 8, groove-like wear is formed, and iron adhesion occurs. Observed. In addition, the ternary oxide component was detected on the entire wear surface in the wear portions of Examples 30 and 32 to 34, whereas the wear portion of Reference Example 1 was a part of the half-moon-shaped wear portion. Only ternary oxides were detected. Incidentally, without addition of ternary oxides, in the case of adding only the type II CaSO ₄ powder (Example 26), the area of the semicircular worn portion of the tool rake face, in Example 30,32～34 It was smaller than that (received with a small area of the tool), and the partial adhesion of iron (Fe) was large. Such iron adherents repeatedly adhere to and fall off from the tool, so that the wear of the cutting tool is likely to proceed or the surface of the work material may not be smooth.

From the above results, it was clarified that the machinability of the sintered body was further improved by using the II type CaSO ₄ powder and the ternary oxide as in Examples 30 to 34.

Claims (8)

  A mixed powder for iron-based powder metallurgy comprising a powder containing anhydrous type II calcium sulfate such that the weight ratio of CaS after sintering is 0.01 wt% or more and 0.1 wt% or less.   2. The mixed powder for iron-based powder metallurgy according to claim 1, wherein the powder containing anhydrous type II calcium sulfate has a volume average particle diameter of 0.1 μm to 60 μm.   The iron-based powder metallurgy mixture according to claim 1 or 2, further comprising one or more ternary oxides selected from the group consisting of Ca-Al-Si oxides and Ca-Mg-Si oxides. powder.   The mixed powder for iron-based powder metallurgy according to claim 3, wherein a weight ratio of the ternary oxide to the sintered CaS is 3: 7 to 9: 1. The volume average particle size of the powder containing anhydrous type II calcium sulfate is Rμm,
When the weight ratio of CaS contained in the sintered body after sintering is W wt%,
The mixed powder for iron-based powder metallurgy according to any one of claims 1 to 4, wherein R ^1/3 / W is 15 or more and 400 or less.   The mixed powder for iron-based powder metallurgy according to any one of claims 1 to 5, wherein the powder containing anhydrous type II calcium sulfate is coated with a lubricant or a binder.   The sintered compact produced by sintering the mixed powder for iron base powder metallurgy as described in any one of Claims 1-6. Producing a powder containing anhydrous type II calcium sulfate by heating a powder containing dihydrate gypsum or hemihydrate gypsum at 350 ° C. or more and 900 ° C. or less;
A method for producing a mixed powder for iron-based powder metallurgy, comprising the step of mixing the powder containing anhydrous type II calcium sulfate and an iron-based powder.